111 lines
2.8 KiB
Ruby
111 lines
2.8 KiB
Ruby
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# Allow an object to alter its behavior when its internal state changes.
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# The object will appear to change its class.
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# Each call to state defines a new subclass of Connection that is stored in a
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# hash. Then, a call to transition_to instantiates one of these subclasses and
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# sets it to the be the active state. Method calls to Connection are delegated
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# to the active state object via method_missing
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module StatePattern
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class UnknownStateException < Exception
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end
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def StatePattern.included(base)
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base.extend StatePattern::ClassMethods
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end
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module ClassMethods
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attr_reader :state_classes
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def state(state_name, &block)
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@state_classes ||= {}
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new_klass = Class.new(self, &block)
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new_klass.class_eval do
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alias_method :__old_init, :initialize
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def initialize(context, *args, &block)
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@context = context
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__old_init(*args, &block)
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end
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end
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@state_classes[state_name] = new_klass
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end
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end
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attr_accessor :current_state, :current_state_obj
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def transition_to(state_name, *args, &block)
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new_context = @context || self
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klass = new_context.class.state_classes[state_name]
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if klass
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new_context.current_state = state_name
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new_context.current_state_obj = klass.new(new_context, *args, &block)
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else
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raise UnknownStateException,"tried to transition to unknown state,#{state_name}"
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end
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end
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def method_missing(method, *args, &block)
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unless @current_state_obj
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transition_to :initial
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end
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if @current_state_obj
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@current_state_obj.send(method, *args, &block)
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else
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super
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end
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end
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end
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class Connection
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include StatePattern
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# you always need a state named initial
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state :initial do
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def connect
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# move to state :connected. all other args to transition_to# are passed
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# to the new state's constructor transition_to:connected, "hello from
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# initial state"
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puts "connected"
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end
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def disconnect
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puts "not connected yet"
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end
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end
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state :connected do
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def initialize(msg)
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puts "initialize got msg:#{msg}"
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end
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def connect
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puts "already connected"
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end
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def disconnect
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puts "disconnecting"
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transition_to :initial
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end
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end
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def reset
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# you can also change the state from outside of the state objects
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# transition_to:initial
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puts "resetting outside a state"
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end
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end
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# Usage
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c = Connection.new
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c.disconnect # => not connected yet
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c.connect # => connected, initialize got msg: hello from initial state
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c.connect # => already connected
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c.disconnect # => disconnecting
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c.connect # => connected, initialize got msg: hello from initial state
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c.reset # => reseting outside a state
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c.disconnect # => not connected yet
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